Turning of a hand wheel at the front of a vertical head band saw machine tilts the column thereof on coaxial trunnions which are journaled in bearings on the rear of the saw carriage. The upper and lower saw pulleys are disposed in the plane containing the column tilt axis, with their axles normal to said plane and supported at zones equidistant therefrom by column carried arms that embrace each pulley. One end portion of each axle is detachable to enable a saw band to be trained over its pulley. A motor drives the upper pulley, and band tension is adjusted by bodily movement of the lower pulley, which is weighted to act as a flywheel.

Current U.S. Class:	83/812
Current International Class:	B23D 53/04 (20060101); B23D 53/02 (20060101); B23D 53/00 (20060101); B27b 013/04 ()
Field of Search:	143/17,17.1,24,30 83/201

Ira Milton Jones

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Claims

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1. A sawing machine having a base with a flat surfaced work supporting table the front portion of which is slitted to accommodate the cutting stretch of a saw band, and a carriage having front and rear portions and constrained to fore and aft translatory motion on the base along a path lengthwise of the slit in its work supporting table, said machine being characterized by: A. a pair of spaced apart rigid front and rear members at the rear portion of the carriage and extending transversely of its path of motion, both of said members being rearwardly of the slitted front portion of the work supporting table in all positions of the carriage; B. a cutting head on the carriage movable bodily fore and aft therewith, said cutting head comprising a column having a portion intermediate its ends accommodated in the space between said transverse members, and a saw blade having a cutting stretch disposed ahead of the foremost of said spaced apart members and substantially parallel to the column with its cutting edge facing forwardly to travel along the slit in the work supporting table during fore and aft movement of the carriage; C. coaxial trunnions projecting horizontally fore and aft from the column; D. and bearings on said transverse members in which said trunnions are journaled, said bearings supporting the cutting head for tilting adjustment relative to the carriage about a horizontal axis substantially coincident with the plane of the flat work supporting surface of the table and parallel to the path of motion of the carriage, and each of said bearings completely encircling the trunnion therein so that throughout its range of tilting adjustment the cutting head is uniformly supported

2. The sawing machine of claim 1 further characterized by saw guiding means constraining the cutting stretch of the saw blade to travel in a plane which intersects the plane of the work supporting surface and also

3. The sawing machine of claim 1 wherein said carriage is substantially U-shaped to provide a bight at its rear which is comprised of said transverse members, and widely spaced apart arms which project forwardly

4. The sawing machine of claim 1 further characterized by: A. the saw blade comprising an endless flexible saw band; B. a pair of pulleys carried by the column and about which the saw band is trained, said pulleys being rotatable about axes which are disposed transversely of the path of the fore and aft motion of the carriage, one of said pulleys being located a distance above the carriage and the other being located below the carriage;

5. The sawing machine of claim 1 further characterized by means for imparting side-to-side tilting motion to the cutting head, comprising: A. an elongated screw mounted on and extending transversely across the carriage at a location below the tilt axis for the cutting head, and constrained to rotate on a horizontal axis adjacent to a portion of said column; B. a nut threaded on said screw; C. a member mounted on the column and constrained to translating motion lengthwise thereof; D. means pivotally connecting said member with the nut whereby rotation of the screw effects tilting of the column on the axis of its trunnions in a direction depending upon the direction the screw is turned; E. and actuator means drivingly connected with the screw to provide for the

6. The sawing machine of claim 5, wherein said actuator means comprises: A. an elongated actuator shaft rotatably carried by the base and extending from the front to the rear thereof; B. a hand wheel fixed to the front of the actuator shaft; C. and meshing bevel gears on the actuator shaft and the screw, the gear on the actuator shaft having a splined driving connection therewith to allow the gears to remain in mesh during back and forth motion of the carriage.

7. A cutting head for a band saw machine comprising upper and lower pulleys carried by an upright column and rotatably on parallel horizontal axes spaced a distance forwardly of the column, and an endless flexible saw band trained around said pulleys, said cutting head being characterized by: supporting structure for each pulley by which the pulleys are held with their axes parallel, and in edgewise vertical alignment and lying on a plane parallel with a vertical median plane through the column, the supporting structure for each pulley comprising: 1. a pair of substantially opposite arms embracing the pulley, both of said arms projecting rearwardly to the column and having force transmitting connections therewith at opposite sides of said median plane; 2. an axle by which the pulley is rotatably connected with the arms, the axle projecting from each side of the pulley and being supportingly connected at its opposite end portions with the arms, so that the axle of each pulley has a force transmitting connection with the column at each side of said median plane, and said supporting structure being further characterized in that; the spacing of the arms from the opposite sides of the pulleys and their respective moments of inertia are such that the band tension load on the pulleys is so divided between the pulley supporting structures at the opposite sides of the pulleys that no lateral deflection or bowing of the column takes

8. The cutting head of claim 7, wherein each of said axles comprises: A. a main axle member rigidly connected to one of its supporting arms; B. a cooperating secondary axle member coaxial with the first axle member; C. means axially separably connecting said main and secondary axle members together; D. and the pulleys being rotatably journaled on said main axle members to be supported thereby at times when the secondary axle members are detached

9. The cutting head of claim 8 further characterized by means on each of said main axle members precluding axial movement of its pulley relative thereto so as to prevent displacement of said pulley at times when the cooperating secondary axle member is detached from its main axle member.

10. In a band saw machine having an endless flexible saw-band trained around spaced upper and lower pulleys that rotate on parallel axes, means supporting said pulleys comprising: A. an upright column; B. a pair of rigid spaced apart opposing arms carried by and projecting substantially horizontally forwardly from each end portion of the column; C. a hub on each pulley, disposed in the space between each pair of arms; D. axle means extending through the hub of each pulley and having end portions supportingly carried by the arms at each side of said hub, the arms and axle means mounting the pulleys with their peripheral portions substantially symmetrical fore and aft with the median plane of the column; E. said axle means for each pulley comprising a main axle member rigidly fixed to one of the supporting arms for said pulley, and a secondary axle member axially slidably mounted in a hole in the opposite arm and having an axially separable screw threaded connection with the main axle member, the pulley being mounted on the main axle member so that it is supported solely thereby when said secondary axle member is detached; and F. each pulley being spaced from the arm supporting its secondary axle member a distance to enable an endless saw band to be trained around its pulley and/or removed therefrom when said secondary axle member is detached from its main axle member.

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Description

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This invention relates to sawing machines and has more particular reference to so-called vertical blade cutoff band saws of the type wherein a carriage mounts an upright cutting head for fore and aft translating movement therewith and for side-to-side tilting adjustment relative thereto so as to enable either straight or angular cuts to be made by the saw as the carriage is translated forwardly along the base of the machine.

The cutting head of such a sawing machine comprises an upright column which is ordinarily supported from the carriage for tilting adjustment about an axis parallel to the path of carriage motion and preferably lying in the horizontal plane of the work supporting surface on the machine. Cutting is performed by an endless saw band trained around a pair of pulleys mounted on the column, one above and the other below the plane of the work supporting surface. The lower pulley is power driven, and since both pulleys rotate on horizontal axes which are normal to the path of carriage motion, the cutting stretch of the band is ordinarily held twisted 90.degree. by suitable guides, to have its cutting edge face forwardly, away from the column on which the pulleys are supported.

Heretofore, the mounting of the column on the carriage for side-to-side tilting adjustment has presented serious problems. In order to assure the desired stability for the cutting head in any of its positions of adjustment, complicated and costly bearing arrangements were resorted to even though assembly of the cutting head on the machine was made more difficult thereby. In some cases, for example, the column was tiltably supported by bearings at both the front and rear of the carriage, one close to the column and the other a substantial distance forwardly thereof. This, of course, required the column to have a forwardly extending boomlike structure for cooperation with an arcuate front bearing. Obviously, the front bearing could not be of a conventional nature if its axis were to lie in the horizontal plane of the work supporting surface.

With the foregoing problem in mind, it is a purpose of this invention to provide exceptionally simple but sturdy means for tiltably mounting the cutting head of a band saw machine on its carriage.

In this respect, it is a more specific purpose of the invention to provide the saw supporting column of a band saw machine with coaxial trunnions that project fore and aft from the column into bearings on transverse rear portions of the carriage between which the column is received.

In band saw machines heretofore available, each of the upper and lower pulley axles was invariably mounted in cantilever fashion from an arm on the column, so as to afford access to one face of its pulley for installation of an endless saw band thereon, or for removal of the band therefrom. No matter how sturdy the column and the wheel supporting arms were made, tensioning of the saw band trained over the cantilever mounted pulleys caused lateral bowing of the column to a degree that could not be tolerated. For that reason, it was customary to provide adjustable bearings for the pulleys, to enable the latter to be realigned and brought into a common plane parallel to the median plane of the column after the saw band was properly tensioned around the pulleys.

In this regard, it is another purpose of the invention to provide a cutting head for a band saw machine of the character described, wherein both of the pulleys around which the saw band is trained are mounted with their peripheries in a common plane which is preferably coincident with the median plane of the column, but in any event parallel thereto; and wherein each is rigidly supported at both sides of the pulley in such a way that the tension of a saw band trained around the pulleys does not tend to cause lateral bowing or deflection of the column on which they are mounted; and the pulleys retain their proper coplanar relationship, in parallelism with the median plane of the column with their axes normal thereto and without need for readjustment of their bearings after the band is tensioned.

Hence, as to this last described feature, it can be said that it is a purpose of this invention to effect a substantial cost reduction through the elimination of expensive adjustable bearing structures for the pulleys, and to simplify the manufacture and the assembly of a sawing machine embodying the invention.

Another and more specific purpose of the invention resides in the provision of a cutting head for band saw machines of the character described, featuring a simple but exceptionally rugged mounting for the band wheels or pulleys around which the saw band is trained, which mounting comprises an axle for each pulley, having opposite end portions supported by pairs of rigid arms carried by the column and extending forwardly therefrom at each side of the pulley; and wherein each axle comprises cooperating axially separable axle members one of which is capable of supporting its pulley while the cooperating axle member is detached therefrom to enable access to be had to one face of its pulleys for training a saw band thereover or for removal of the band therefrom.

Still another object of the invention resides in the provision of a band saw machine of the character described, wherein for the first time, the upper of the two band wheels or pulleys is driven from a suitable prime mover to achieve a number of advantages heretofore unattainable. Chief among these advantages are the simplification of the pulley drive train and the drive cover design; and location of the drive train in a cleaner area, above the zone at which sawing takes place.

These desirable features of the invention are made possible to a considerable extent by another innovation in band saw machine design, namely the provision of an idler or lower pulley which is weighted to achieve a fly wheel effect that overcomes any tendency for the cutting stretch of the band to vibrate when cutting through a work piece. Such vibration might otherwise result from the fact that the cutting stretch of the band is pulled through the work by its opposite or noncutting stretch, giving rise to somewhat greater elongation of the band during sawing than obtains when the cutting stretch of the band is pulled through the work by the drive pulley.

A further object of the invention resides in the provision of improved and simplified means for effecting tensioning of a saw band trained over the pulleys. Heretofore, this was accomplished by means which involved mounting the upper pulley on a vertically adjustable bearing, and which necessitated costly and accurate machining of close fitting surfaces on the bearing and guides between which it was slidably received.

In connection with the object of the invention broadly stated in the preceding paragraph, it is a more specific object of the invention to provide a cutting head for a band saw machine of the character described, wherein the lower band wheel or pulley is rotatably supported on the outer end of the horizontal arm of a bell crank lever which is pivotally mounted on the lower end of the column for rocking motion about an axis parallel to the pulley axis, and which has an upright arm extending upwardly alongside the column and operatively connecting with force applying means to enable the lever to be rocked in a band tightening direction about its axis.

Still another purpose of the invention resides in the provision of means which is actuatable from the front of the machine for effecting side-to-side tilting adjustment of the cutting head through mechanism connecting with the rear of its upright column.

With these observations and objects in mind, the manner in which the invention achieves its purpose will be appreciated from the following description and the accompanying drawings. This disclosure is intended merely to exemplify the invention. The invention is not limited to the particular structure disclosed, and changes can be made therein which lie within the scope of the appended claims without departing from the invention.

The drawings illustrate one complete example of the physical embodiment of the invention constructed according to the best mode so far devised for the practical application of the principles thereof, and in which:

FIG. 1 is a side elevational view of a vertical blade band saw machine embodying this invention, portions thereof being broken away to show internal construction;

FIG. 2 is a front elevational view thereof, indicating in construction lines the extent of side-to-side tilting adjustment of which the cutting head is capable;

FIG. 3 is a sectional detail view, at an enlarged scale, taken on the plane of the line 3-3 in FIG. 1;

FIG. 4 is a cross-sectional view, at an enlarged scale, taken on the line 4-4 in FIG. 1 and showing the mechanism for effecting tilting of the cutting head;

FIG. 5 is a sectional detail view taken on the line 5-5 in FIG. 4, and at an enlarged scale;

FIG. 6 is a more or less diagrammatic perspective view showing the drive mechanism for the upper pulley;

FIG. 7 is a fragmentary side elevational view showing how the carriage supports the cutting head for fore and aft bodily motion therewith and for side-to-side tilting motion relative thereto;

FIG. 8 is a fragmentary perspective view illustrating the structure seen in FIG. 7;

FIG. 9 is an enlarged detail view partly in section and partly in elevation, illustrating the axle mounting for each pulley;

FIGS. 10, 11 and 12 are diagrammatic views illustrating the bowing effect of band tension on the cutting head of a conventional vertical blade band saw machine; and

FIG. 13 is a diagrammatic view similar to FIGS. 10, 11 and 12 but illustrating how the hitherto undesirable bowing effects of band tension on the column are overcome in the band saw machine of this invention.

Referring now to the accompanying drawings, the numeral 15 generally designates the elongated base structure of what can be termed a vertical blade band sawing machine which embodies this invention. Mounted on the top of the base is a work table 16, the forward portion of which affords a horizontal work supporting surface 17. Front and rear vises 18 and 19 supported on and adjustably securable to the front portion of the table are adapted to hold a work piece 20 in a fixed position upon the work supporting surface while a saw cut is made therein or therethrough. A narrow slot 21 extending fore and aft through the front portion of the table accommodates the blade 22 of the saw.

Since the saw of this invention is intended primarily as a cutoff saw for cutting through relatively long work pieces, such as long lengths of structural steel, the work table 16 is generally flanked by work supports 16a and 16b as partially shown in light lines in FIG. 2. These flanking work supports usually are quite long and often have power driven rollers to advance the work to and carry it from the cutting zone.

The saw blade 22 is an endless band which is trained around upper and lower band wheels or pulleys 23 and 24, respectively and which, together with an upright column 25 from which the pulleys are supported, comprise the cutting head 26 of the machine.

The cutting head is mounted upon a U-shaped carriage 27 having opposite parallel reaches 28 which are horizontally disposed and lie inwardly adjacent to longitudinal rails 29 fixed to the top of the base 15. The reaches 28 are rigidly joined together by the bight 30 of the U-shaped carriage, which bight is located at the rear of the carriage and comprises a pair of transvers bridge members 31 spaced from one another a distance to readily receive the column 25 of the cutting head therebetween. Rollers 32 mounted on the reaches and tracking on edge and side surfaces of the rails 29 constrain the carriage to fore and aft translatory motion along a horizontal path extending lengthwise of the base.

The carriage normally occupies a retracted position such as seen in FIG. 1, at which its bight 30 is closely adjacent to the rear of the base 15. In the foremost position of the carriage seen in construction lines in FIG. 1, the bight 30 of the carriage will have advanced to a zone substantially midway between the ends of the base. The opposite reaches 28 of the carriage, of course, are disposed beneath the table 16, near the opposite sides thereof.

More or less conventional upper and lower saw guides 34 and 35 are rigidly carried by the column 25 for engagement with the forward or cutting stretch of the saw band 22. While the lower guide 35 can be mounted at a fixed level below the work supporting surface, the upper guide is adjustable up and down in the usual manner, to accommodate work pieces of different heights during sawing. Sawing is accomplished by forward translation of the carriage and the cutting head 26 thereon, but since the band wheels or pulleys rotate on parallel horizontal axes normal to the path of carriage travel, the saw guides must hold the intervening cutting stretch of the saw band twisted 90.degree. with the toothed edge thereof facing forwardly, away from the column 25.

One of the features of the band saw machine of this invention resides in the unusually simple manner in which the cutting head 26 is pivotally supported by the carriage 27 for side-to-side tilting adjustment out of vertical, to canted positions necessary for making angled or miter cuts in a work piece. This pivotal support comprises coaxial trunnions provided by the end portions of a short shaft 37 which extends horizontally fore and aft through a central portion of the column 25, to which it is welded or otherwise secured. These trunnions are journaled in coaxial bearings 38 secured to the transverse bridge members 31, between which the column is received. The bearings 38 provide the sole support for the cutting head; and since accurate cutting in any and all positions of the cutting head requires that the plane of the cut made by the saw always intersects the plane of the work supporting surface 17 on the same line, the axis of the bearings 38 coincides with the line of intersection between the cutting plane and the plane of the work supporting surface. Although this requirement has been met in tilting type cutoff saws heretofore available the bearing structures which defined the tilt axis in those earlier machines were considerably more complicated than the simple bearings of this invention.

Since the column is of tubular construction, being substantially rectangular in cross section, it is preferably reinforced by front and rear plates 39 at that portion thereof from which the trunnion defining ends of the shaft 37 project. Also, because the main portions of the carriage are located below the table 16, the bearings 38 are carried by brackets that are secured by screws to pads 40 on the tops of the transverse bridge portions of the carriage, and are of a height to dispose the axis of the bearings in the plane of the work supporting surface 17.

The space between the transverse bridge members 31 allows tilting of the column a full 45.degree. to each side of a normal vertical position, as indicated in FIG. 2. The rear portion of the table, of course, has a centrally located longitudinal cutout 41 therein wide enough to accommodate the column in any position of adjustment thereof about its tilt axis, and long enough to accommodate the bearings on the carriage throughout its entire range of fore and aft movement along the base.

The cutting head can be accurately moved to and held in any desired position of adjustment on its tilt axis by structure best illustrated in FIG. 4. As therein seen, laterally directed forces can be applied to a portion of the column 25 at a location spaced a distance below its tilt axis, in consequence of rotation of a screw 43 in one direction or the other. The screw 43 extends transversely and horizontally across the rear of the carriage 27, behind the column 25, and has its end portions journaled in depending flanges 44 on the carriage by bearings which preclude axial motion of the screw relative to the carriage. A nut 45 threaded on the screw can be translated lengthwise thereof in one direction or the other, depending upon the direction the screw is rotated, providing the nut is held against rotary motion with the screw. For this purpose, the nut 45 is pivotally mounted on a stud 46 projecting rearwardly from a block 47 which is mounted on the rear of the column and constrained to motion lengthwise of the column by ways 48 thereon, between which the block is slidably received.

Hence, the stud 46 not only prevents rotation of the nut on the screw 43, but it also translates rotation of the screw into pivotal motion of the column about the axis of its shaft 37, through the connection it affords between the nut and the slide block 47.

One end portion of the screw is extended as at 50 and has a bevel gear 51 fixed thereto at a location adjacent to one side of the base 15. A companion bevel gear 52 meshing with the gear 50 is slidably splined to an actuating shaft 53 that extends forwardly all the way to the front of the base, where it has a universal joint connection 54 with the spindle of a hand wheel 55 carried by the base. A housing 56 having bearings through which the screw extension 50 and the actuating shaft project, serves as an enclosure for the bevel gears 51 and 52 and also holds the same in meshing engagement as the carriage and the cutting head thereon is translated fore and aft along the base.

With the structure described above, mechanism at the rear of the column is operable to adjust the cutting head on its pivot axis, in consequence of rotation of a hand wheel at the front of the machine. Precise adjustment of the angle of tilt for beveled cuts is assured by employing a screw 43 with fine threads thereon; and the tilt angle can be accurately ascertained by means of a protractor 57 such as indicated in FIG. 4.

It is conventional in band saw machines of the type herein concerned to drive the lower of the two band wheels or pulleys about which the saw band is trained, and to provide for obtaining the proper tension on the saw band by making the bearing for the upper pulley adjustable up and down with respect to the column from which it is supported. The present invention departs from the conventional in these respects in that it provides for band tensioning adjustment of the lower pulley 24 and for driving the upper pulley 23, to achieve certain significant advantages which will appear shortly.

The upper pulley 23 is driven from a prime mover 58 which is mounted in an enclosure 59 that is secured to the column 25 at a location near the level of the upper pulley. The prime mover can be an electric motor having a multiple V-groove drive sheave 60 on its shaft 61. The drive sheave 60 is located adjacent to one side of the column 25, rearwardly in line with another multiple groove sheave 62 which is fixed to one end of a short shaft 63 extending across the front of the column. The shaft 63 is journaled in a bearing 64 on the front of the column for rotation on a horizontal axis parallel to that of the motor shaft 61. A V-belt 64 engaged in selected grooves in the sheaves 60 and 62 drivingly connects the shaft 63 with the motor.

Fixed to the other end of the shaft 63, at the opposite side of the column 25, is another sheave 65 which is drivingly connected by a belt 66 with a larger sheave 67 fixed to one end of a pulley drive shaft 68. The pulley drive shaft is supported from the column 25 for rotation on a transverse axis parallel to and coplanar with the axis of the upper pulley 23, just behind its periphery. A more specific reference will be made later to the manner in which the pulley drive shaft 68 is supported from the column. It is here sufficient to point out that the pulley drive shaft has a drive pinion 69 fixed to its end remote from sheave 67, and in meshing engagement with the teeth of a larger gear 70 on the flanged periphery of the upper pulley 23. The usual housing structure 71 encloses the upper pulley and all of its drive train except the belt 64 trained over the motor sheave 60. This last named belt can be housed within the motor enclosure 59.

In the pulley drive arrangement described, the forward or cutting stretch of the saw band is moved downwardly during sawing in consequence of the pull which the power driven upper pulley exerts upon both the cutting and the noncutting stretches of the saw band. Since the saw band is, in effect, a spring that stretches under load, the increased length through which the pull on its cutting stretch is exerted can tend to cause vibrations which cannot be tolerated. In order to overcome any tendency for such vibration, this invention provides a lower band wheel or pulley 24 which is weighted to an extent sufficient that its increased mass and inertia enables it to achieve a flywheel effect during sawing. Thus, the tension can be maintained substantially uniform on the cutting stretch of the blade, and vibration is effectively precluded.

A simple shielding device 73 can be applied over the lower pulley 24 to protect it from metal shavings produced during sawing. It should be noted, however, that the power driven pulley 23 and its drive mechanism are located in a clean area, a distance above the cutting zone, where no special shielding is required.

According to this invention, the band wheels or pulleys 23 and 24 are supported by structure that is vastly superior to the conventional cantilever supporting means heretofore employed in band sawing machines of this nature. Such conventional cantilever pulley supporting structure inevitably disposed the pulleys at one side of the column, in offset relation thereto, and thus made it essential to provide complicated rockable pulley bearings that had to be tiltably adjusted relative to the column after tensioning of a saw band around the pulleys, to bring the latter into edgewise alignment and thereby compensate for the lateral bowing or distortion that occurred in the column as a result of band tension. This condition is diagrammatically illustrated in FIGS. 10, 11 and 12, which represent a typical cantilever mounting of the upper and lower band wheels or pulleys 23 and 24 in adjustable bearings B on one side of arms A extending forwardly from the column C.

FIG. 10 illustrates the straight condition of the column C and the edgewise alignment of the upper and lower pulleys that obtains before the saw band22' is tensioned. When the band is properly tensioned, its pull upon the offset pulleys causes the column C to bow or deflect laterally as illustrated in exaggerated form in FIG. 11, so that the axes of the upper and the lower pulleys are no longer parallel and the pulleys are out of the edgewise alignment desired. It is at this time that the bearings B for the pulleys must be adjusted relative to the column, as indicated in FIG. 12, to bring the axes of the pulleys back into parallel relationship. It will be apparent, therefore, that special and costly adjustable bearings were essential in conventional band saw machines; and that considerable time had to be spent in tedious readjustment of the bearings each time it was necessary to replace a band, and especially if the new band was of different width or cutting characteristics, requiring a different tension load.

FIG. 13 diagrammatically illustrates the mounting for the band wheels or pulleys in the sawing machine of this invention, which mounting is such as to eliminate the tendency for the column to bow laterally under the tension of the saw band upon the pulleys. As will now be described, this feature of the invention is achieved by rigidly supporting the pulleys 23 and 24 at their opposite sides, with their peripheries in a common plane which may be coincident with the median plane of the column 25, but in any event is parallel thereto. Specifically each pulley is journaled on an axle 77 that is jointly carried by a pair of rigid spaced apart parallel arms 75 and 76 that project forwardly from the column, Each pair of arms embraces one of the pulleys.

If the arms of each pair are equispaced from the common plane of the pulleys and also equidistant from the median plane of the column, as is the case in the embodiment of the invention illustrated in the drawings, the pulley supporting structure at each side of each pulley-which consists of the arm and adjacent end portion of the axler-carries exactly one-half of the band tension load on the pulley, and therefore the pulley supporting structures at both sides of the pulley would have to have the same moment of inertia. Obviously, though, the arms need not be symmetrical to the median plane of the column. The only important consideration is that the pulley supporting structures at the opposite sides of the pulleys be designed to carry their share of the band tension load imposed thereon. In other words, if the supporting structures are not equidistant from the median plane of the column and the plane of the pulleys, so that the loads imposed thereon by band tension are not equal, this difference in loading can be compensated by designing the supporting structures with correctly calculated different moments of inertia-the supporting structure at one side of the pulley would simply have to be stronger than the other.

In any event, the band tension load on the pulleys is so divided between the pulley supporting structures at the opposite sides thereof, that no lateral deflection or bowing of the column takes place and the pulley axes remain parallel.

The arms 75 - 76 between which the upper pulley is mounted, can be straight flat bars having their rear end portions flatwise overlying the opposite sides of the column and rigidly fixed thereto as by welding. They project horizontally forwardly from the column, to opposite sides of the upper pulley 23, and their outer end portions are apertured to receive and support the opposite end portions of the upper pulley axle 77.

The upper arms 75--76 also provide supports for the pulley drive shaft 68, which projects through them and is rotatably journaled in suitable bearings carried thereby (see FIG. 1).

Though FIG. 9 shows the mounting for the lower pulley 24, the axles for both pulleys are substantially identical. Each axle is comprised of cooperating axially separably connected main and secondary axle members 78 and 79 respectively. The main axle member 78 is stepped to provide a larger diameter end portion 79 which projects axially from one side of the pulley through a hole 80 in the adjacent arm 75 to a flange 81 on its outer end. The flange 81 can be integral with the main axle member, and it is secured as by screws 82 to the outer face of its supporting arm so as to rigidly mount the main axle member thereon.

The smaller diameter inner portion 83 of the main axle member 78 projects through the hub 84 of the pulley and receives ball bearings 85 by which the pulley is freely rotatably supported by the main axle member. One of the bearings abuts the shoulder 86 at the junction between the smaller and larger diameter portions of the main axle member, and a spring ring 87 snapped into a suitable groove in the extremity of the smaller diameter axle portion 83 cooperates with the shoulder 86 to prevent axial movement of the pulley relative to the axle.

The end portion of the main axle member which is encircled by the pulley is hollow and provides an axially elongated socket 89 to snugly but rotatively receive a reduced end portion 90 on its cooperating secondary axle member 79. Screw threads 91 formed on the extremity of the reduced portion 90 and cooperating with complementary threads in the bottom of the socket 89 hold the main and secondary axle members assembled, with a shoulder 92 on the secondary axle member engaging the extremity of the smaller diameter portion 83 of the main axle member.

The secondary axle member 79 extends axially outwardly through a hole 93 in its adjacent arm 76 to thus receive support therefrom. A handle 94 fixed to the secondary axle member and accessible from the exterior of its arm 76 facilitates rotation of the secondary axle member in the direction to effect axial separation thereof from the main axle member at times when access must be had to the pulley to train the saw band thereover or to remove the band therefrom.

It should be observed that the pulley supporting arms 75 which carry the main axle members 78 are strong and rigid enough to alone bear the load of band tension on the pulleys and thereby prevent damage to the machine in the event an operator inadvertently fails to replace the secondary axle members before tensioning the saw band on the pulleys. Though this will prevent damage to the machine, it will not necessarily assure the edgewise alignment of the pulleys essential to keep the saw band running true. As a result, this omission will be quickly detected by the operator, and corrected by replacement of the secondary axle members 79.

The lower pulley 24 is bodily adjustable up and down, so that the saw band can be tensioned in consequence of downward movement thereof. For this purpose, it is supported by a bell crank lever 96, of which the opposite arms 75 and 76 described earlier form a part. The arms 75 and 76 of the bell crank lever project substantially horizontally from opposite sides of the column to which they are pivotally connected by a stub shaft 97. The bell crank lever also comprises opposite upright arms 98 which are rigidly connected to the pivoted ends of the horizontal arms and extend upwardly alongside the column, at opposite sides thereof, to a point a short distance above the base. Their upper ends are joined by a bail 99 which extends around the rear of the column, in spaced relation thereto. A hand wheel 100 having its stem 101 threaded into the rear of the column, is operatively connected to the bail as at 102 so that rotary motion of the wheel in one direction causes counterclockwise pivotal motion of the bell crank lever and tensioning of a saw band trained around the pulleys. Rotary motion of the hand wheel in the opposite direction, of course, effects clockwise swinging motion of the bell crank lever to relax the tension of the saw band.

From the foregoing description, together with the accompanying drawings, it will be readily apparent to those skilled in the art that this invention provides a band saw machine which not only constitutes a substantial improvement over the conventional, but which is also simpler and less costly.

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